Index

Mobile communications page

    Introduction to modern mobile communications

    The most modern telephone is the cellular telephone, or commonly called a cell phone. A cellular telephone is designed to give the user maximum freedom of movement while using a telephone.Mobile communications is a hot topic. The number of mobile communicationdevices users is growing very fast. The number of mobiles (cellular phones)is now exceeding the number of fixed lines in many countries(Finland, Japan etc.).Cellular/mobile phones are everywhere and their utility is growing. A cell phone is a radio telephone, that may be used wherever "cell" coverage is provided. The role of cellular phones has risen with improvement in services, reduction in service costs and the ever increasing services available through cell phones.Mobile Internet access is a global phenomenon with even great implications.Leading phone manufacturers such as Ericsson, Matsushita (Panasonic), Motorola, and Nokia have put a great deal of marketing effort behind the mobile Internet phenomenon, recognizing that adoption is a complex business proposition. In Europe, WAP is has generated widespread interest because of lots of marketing and expectations put to it. In Japan NTTDoCoMo's mobile Internet service is based on a service called iMode that uses Compact HTML (CHTML) microbrowsers in the phone.There are also products on the market which combine a PDA, a real web-browser and some communication interface (cellular phone, WLAN etc.) into one smart communication device. A the generic phone may soon acquire a browser. And mobile phones will morph into PDAs or organizers. The markets will show what customers will buy and use. The handsets sold over the next few years are likely to operate much differently than those of today. Mobile terminals are complex embedded systems, with stringent real-time requirements for signaling and voice processing. Now Web browsing, multimedia, and connectivity requirements are added to the list.There are many technical challenges to be solved to make all this to work.Ubiquity is a pinnacle that the cellular communication sector has hoped to reach for the past five years. To reach this goal, a series of networks must be built that allow consumers to use their phone anytime, anywhere.The truth is ubiquity is far from becoming a reality. Across the world cellular carriers can't seem to agree on a single air interface for wireless operation.But, despite battles on the standards front, the wireless community has pushed forward in its efforts to build mobile networks and phones that deliver worldwide coverage. To make this happen, they have focused their attention on developing multimode systems that can support CDMA, TDMA, GSM, GPRS, wideband CDMA (W-CDMA), and a host of other air interfaces in the same box. Nowadays the mobile communication technology seems to be divided to differente generations of technologies. A short description thosegenerations are the following:

    • 1G (first generation): This described the early analogue cellular phone technologies. For example NMT and AMPS cellular technologies belong to this category.
    • 2G (second generation): This described the generation of first digital fidely used cellular phone systems. GSM technology is the most widely used 2G technology. This gives you digital speech and some limited data capabilities (circuit switched 9.6 kbit/s). Other 2G technologies are IS-95 CDMA, IS-136 TDMA, and PDC.
    • 2.5G (two and half generation): This is an enhanced version of 2G technologies. This gives higher data rate and packet data services. GSM system enhancements like GPRS and EDGE are considered to be 2.5G technologies. The so-called "2.5G" systems represent an intermediate upgrade in data rates available to mobile users.
    • 3G (third generation): Third generation mobile communciation systems often called with names 3G, UMTS and W-CDMA promise to boost the mobile communications to new speed limits. The promises of third generation mobile phones are fast Internet surfing, advanced value-added services and video telephony. Third-generation wireless systems will handle services up to 384 kbps in wide area applications and up to 2 Mbps for indoor applications.
    • 4G (fouth generation): It has not been widely defined what this is. 4G is intended to provide high speed, high capacity, low cost per bit, IP based services. The goal is to have data rates up to 20 Mbps. Most propable the 4G network would be a network which is a combination of different technologies (current celluart networks, 3G celluar network, wireless LAN, etc.) working together usign suitable interoperability protocols (for example Mobile IP). There are also views that 4G could be some entirely new radio access technology.
    • 5G (fifth generation): There is no clear definition what this is. This wil be somethign more advnaced than 4G.
    In mobile communication there are three sectors on the field: telecom companies who operate the networks, cellular phone makes who make the phones and companies which make the devices for the cellular phone networks. All of these businesses are big. For example around 400-600 million ceullar phones are sold in one year in the world. Some of the largest companies in the field(for example Nokia and Ericsson) make both networks and cellular phones. Today Mobile Internet is a hot topic. Mobile Internet benefits from the creativity and enthusiasm of entrepreneurs to bring life to the market. It is not only the technology, but a multitude of consumer and business issues, which will decide how quickly and widely next-generation wireless services are deployed.The first version of WAP was a dissappointment to users, because it was not real Internet, but some poor imitation of it. The first users got a very strong dissappointment on the services, and the service market has not got any gib business although most new cellular phones have WAP capabilities in them, but hardly anyone uses them in most countries. Instead of WAP, most users use SMS to access simple mobile services.In Japan, mobile Internet is getting a warm reception for various reasons in busines, technology and marketing. Third Generation wireless services are being boosted by a combination of positive factors in Japan. The Japan government is now pushing for third generation (3G) services, both to provide increased mobile capacity at home, and to ensure that Japanese companies are well positioned in the competition for the next generation of wireless equipment around the world. Before 3G there could be 2.5G.In Europe, deployment of modified second generation services (called 2.5G products) such as General Packet Radio Service (GPRS) will boost bandwidth and provide always-on capability that should make the mobile Internet take off. GPRS is an attractive solution to operators, because it does not require the same degree of investment as UMTS. In Europe licenses for operators for third generation (3G) services have been sold in many countries at very high prices to operators, and not operators have some hard time in figuring out how to get the money from user to play for the ghigh licensing fees and high cost of building 3G network. In North America, recently announced wireless data services (such as Sprint's HDML based web browsers) are creating U.S. market awareness. America is well behind Europe and Asia in mobile adoption, let alone wireless data services. Size and wealth make the U.S. a very attractive target, but the hyper-competitive business environment has actually held U.S. adoption back.
    • 3G (third generation): Third generation mobile communciation systems often called with names    Rate this link
    • 4G (fouth generation): It has not been widely defined what this is. 4G is intended to provide high speed, high capacity, low cost per bit, IP based services. The goal is to have data rates up to 20 Mbps. Most propable the 4G network would be a network which is a combination of different technologies (current celluart networks, 3G celluar network, wireless LAN, etc.) working together usign suitable interoperability protocols (for example    Rate this link

    History

    The origins of radio communications are in the 19th century.

    • 1864 James Clerk Maxwell presented the Maxwell Equations for electromagnetic radiation
    • 1876 Alexander Graham Bell invented the telephone.
    • 1887 Heinrich Hertz discovered "hertzian waves" which are now called as radio waves.
    • 1896 Guglielmo Marconi carried out the world?s first radio transmission.
    At the beginning of our century, e.g. the police forces in Europe and in the US were using radio telephony equipment. During the 50?s and 60?s, first radio telephone networks were introduced for public customers in the US.As the radio telephony services became more popular, the insufficient availability of radio frequencies became obvious. At the 60?s and 70?s, new technologies like dynamic channel allocation and cell-based networks were developed in order to decrease the congestion in the radio frequencies. The increasing lack of frequencies in the radio telephone services led to the development of cellular networks in the 70?s. The Bell Telephone company (US) introduced the first cellular public network AMPS (Advanced Mobile Phone Service) in 1978. It became a single standard for North America in 1982. The idea behind cellular networks is the sub-division of a geographical area covered by a network into a number of smaller areas called cells. The frequencies allocated to one cell can be reused in other cells that are far enough not to disturb. A fixed radio station called as a base station within each cell acts as a transmitter/receiver serving all the mobile stations inside the cell area. A base station controls a group of transmitting/receiving frequencies allocated by the network to that cell. In the 80?s, several analogue cellular radio networks entered to service around the world. Each country has proceeded in its own way in adopting standards for these networks. These standards are not mutually incompatible.Later international standards, like GSM, were introduced. The generations of different cellular technologies were introduced after each other.
    • 1st generation: analogue transmission: AMPS (Advanced Mobile Phone System) in USA, TACS (Total Access Communication Service) in Europe, NMT (Nordic Mobile Telephone), and others
    • 2nd generation: digital transmission: GSM (Global System for Mobile Communications), ERMES (European Radio Messaging System) - paging, CT2, CT3 (Cordless Telephone Standards), DCS 1800 (Digital Communication Service), DECT (Digital European Cordless Telephone)
    • 3rd generation: unification of different technologies: FPLMTS (Future Public Land Mobile Telecommunication System), UMTS (Universal Mobile Telecommunication System), IMT-2000 (International Mobile Telecommunication)

    Basic technologies

    The vast majority of today's voice-only (2G) wireless communications devices were originally based on a dual-processor architecture. A digital signal processor (DSP) handled many of the communications tasks, such as modulating and demodulating the bit stream, coding and decoding to maintain the robustness of the communications link despite transmission bit errors.In addition DSP part usually handles encrypting and decrypting for security, and compressing and decompressing the signal. The second processor was a general-purpose processor, which processed the user interface and the upper layers of the communication protocol stack. The basic dual-processor architecture of 2G will migrate to data-centric 2.5 and 3G devices, but needs to be enhanced.New 2.5 and 3G applications, such as streaming video and others, will change the nature of wireless communication devices. Designers of wireless platforms should be concerned about maintaining a high degree of flexibility.

      Radio access technologies

      Cellular phone systems use radio access technologies to make the wireless connection between your cellular phone and the base station servicing you at the moment. Modern cellular systems use genrally duplex radio links. They use two different frequencies to communicate. The base station transmits at one frequency, and the cellular phone listens to this. The phone transmit at another frequency, and base station listens to this. Two different radio frequecies are use to be able to make the cellular phone and phase station to transmit and receive signal at the same time without those signals interfering with each other. This how majority of the analogue and digital cellular system work. There is a limited set of frequencies use for transmission and reception and those are called radio channels. In analogue system when phone makes a call, it takes into use one transmitting frequecy and one reception frequency (what the phone uses is controlled by the cellular network). In digital systems the idea is the same, but the modern system allow many phones to share the same frequency using time dividion multiplexing (each phone has a defined timeslow when it can receive and transmit it's data packets, thus many phone can use the same frequency, each at different times). There are limit to the maximum distance from phone to base station communications. The signal power generated by transmitter, receiver sensitivity, antenna performance, distance, attenuation caused by environment and noise in then used frequency band define how long the signal can travel until it becomes unusable. Depending on the environment the signal coverage from the base station to phone can be from few hundred meters up to tens of kilometers. The impairments in radio transmission are difficult to model dynamically because of their unpredictable nature. Typical impairments are:

      • The absorption of radio signal power (air and surrounds absorb signal)
      • Signal refelctions caused by the ground and obstacles (signal detected in the receiver is a sum of direct and reflected waves which can cause an effect known as fading)
      • Co-channel interference (distant radio transmitters on the same frequency will disturb the reception)
      • Intermodulation distortion (transmitters on different frequencies can disturb each other)
      • Background noise in receiver (thermal noise generated by the receiver electronics itself)
      • Atmospheric noise (bursty noises from thunder storms and similar)
      • Industrial noise (RF noise from electronics, sparks)
      Very often the link a mobile phone maintains is limited mainly by the power the phone itself can radiate in order to make itself heard by the base station. The other direction signal (base station to phone) is not usually the bottleneck as the base stations can generally crank out as much power as needed (they have generally much more powerful transmitters than the phones). When the link form phone to base station does not work, things that can be done, are re-arranging the antenna so that less power is needed (use the antenna on the roof of a car or house for example), or using a more efficient antenna (eg. a Yagi-Uda), or effectively increase the output power of the phone. What user can do is generally limited to what he/she can do with the antenna, because generally the user can't increase the cellular phone transmitting level. Other thigns the operator can do to increase the base station coverage is to use higher gain antennas in the base statio receiver or using a more sensitive receiver. In case you need to do something to make the cellular phone reception better in your case is to use the following advice: Usually the only thing that will help you is an external antenna. Buy a $20 Yagi antenna for the frequency band of your cellphone standard, mount the antenna on a 10 foot mast on the roof of your house, turn the antenna in the direction of the nearest base station, and connect that antenna to your phone. Car-kits of your mobile phone supplier work the best. You will get an enormous improvement in reception. Before doing this anythign on this first get enough technical knowledge so that you can do the connection right so that your antenna does not break anything in your phone, cause interfernce or cause any other safety hazard. Check also that it is legal to use the antenna you consider to use with your phone (there can be some legal limitations on some countries what kind of antennas are allowed to be connected to cellular phone legally).

      Antennas

      Antennas are critical links in the wireless signal chain.Right antenna for the application yields a good signal coverage, increased S/N ratio, reduced bit error rate, and lower power consumption all at very low cost.As cellular telephones have evolved over the years, so have their components, particularly the antennas. Cellular phone used to have large external antennas, but nowadays most cellular phones use an internal antenna. Consumers do not (and should not have to) understand antenna theory, but design engineers needs to understand it. . An antenna is fundamentally a transmission line that transforms information from electrical energy (current and voltage) into electromagnetic energy (RF waves). The length of this line is inversely proportional to the frequency of transmission. Therefore, as new wireless applications in the past moved up in the frequency spectrum (Commercial Radio, Broadcast Television, Analog Cellular, Digital PCS, Wireless Data), their antennas correspondingly decreased in size. As an example, a 1/4-wave 4-inch analog cellular "whip" antenna at 800 MHz becomes a 1.5-inch digital PCS "stubby" antenna at 1900 MHz. Old cellular used monopole used retractable antennas (stubby antennas).This kind of monopole antennas are implemented using lambda/4 length. They are the antennas of choice for wireless device designers implementing an external antenna. Typical antennas you will see in more modern cellular is a helix radiator using 1/4-wave or 1/2-wave resonances. The cellular phone antenna radiator is mounted on a plastic carrier, the antenna is a solid and compact unit. On dual band antennas usually 1/4-wave is used for GSM and 1/2-wave for DCS/PCS. Those antennas are generally matched for 50 ohm impedance. A rapid growing market for wireless communication has create a remarkable trend towards the development of integrated antennas for mobile phones. Many modern small cellular do not use external antennas anymore. Those cellular phones use a tiny planar or otherwise miniature special antenna which can be embedded into the phone plastic case. Antennas are slowly becoming more integral as new antenna technology becomes available. Today there are four leading antenna architectures that are commonly used in embedded applications: microstrip, patch, Planar Inverted 'F' Antenna (PIFA) and Meander Line Antenna (MLA).Microstrip lines are an extension of the monopole. They can be easily fabricated by etching a copper strip of 1/2- or 1/4-wavelength onto the radio circuit board. While very inexpensive to make, its performance is limited by surrounding electronics on the circuit board. Microstrip is also only a single-frequency solution.Patch antennas are a good choice for a system that requires a beam pattern focused in a certain direction. Patches are fabricated out of square or round copper clad on the top surface of a circuit board. Their radiation beam is normal to the surface of the board.One antenna type becoming increasingly popular is PIFA (planar inverted-F antenna). The PIFA antenna literally looks like the letter 'F' lying on its side with the two shorter sections providing feed and ground points and the 'tail' providing the radiating surface. PIFAs make good embedded antennas in that they exhibit a somewhat omnidirectional pattern and can be made to radiate in more than one frequency band. PIFA has a low profile, and it can easily be incorporated into wireless handsets.PIFA antennas are generally used with a ground plane, which is generally the cellular phone circuit board ground plane. The MLA (Meander Line Antenna) is a new type of radiating element, made from a combination of a loop antenna and frequency tuning meander lines. The electrical length of the MLA is made up mostly by the delay characteristic of the meanderline rather than the length of the radiating structure itself. MLAs can be designed to exhibit broadband capabilities that allow operation on several frequency bands. For the base stations classical dipoles are very common. The common dipole has long been recognized as an efficient radiator when cut to the appropriate frequency length. It is made from bending the end of an open circuit two-wire transmission line into a 'T' shape, where the top of the 'T' is the radiating section of the antenna. The length of the top is lambda, the wavelength of the signal. In some applications also monopole antennas with lambda/2 or lanbda/4 length mounted over ground plane are used. There are also special antenna constructions for special applications. When you need to flood a wide but defined area with RF energy, such as for perimeter security systems, tunnels, and cellular- or 802.11-system interior zones, one approach is to use an RF-leaky feeder cable to provide controlled radiation.

      Cellular network

      The idea behind cellular networks is the sub-division of a geographical area covered by a network into a number of smaller areas called cells. The frequencies allocated to one cell can be reused in other cells that are far enough not to disturb. A fixed radio station called as a base station within each cell acts as a transmitter/receiver serving all the mobile stations inside the cell area.A base station controls a group of transmitting/receiving frequencies allocated by the network to that cell. The base station has also the control over subscribers that are currently in the cell area. When a subscriber wants to make a call, the base station allocates a transmitting frequency which is then used between the subscriber and the base station. When the subscriber moves into another cell, a handover takes place, and a new base station takes over the control of the call and assigns a new frequency that is different from the first. The original frequency used in the first cell is released. The cellular concept enables the following features:

      • Reduction of mobile terminal and base station transmitting power compared to many other radio systems
      • The dynamic allocation of frequencies during the call
      • The reuse of frequencies in cells separated far enough apart
      • Increased number of subscribers

      Signal processing

      Modern mobile communications used lots of very heavy signal processing. Signal processing is generally done in speed coding and for doing complex data signal modulation/demodulation. Signal processing is generally done with DSPs, FPGAs and special ICs.

      The digital cellular phones allow voice communications using quite low bit rates. The voice codec system used on digital cellular phone systems allow efficient compression of voice data. The GSM codec, indeed most voice codecs used nowadays, compress the signal by modeling the human voice tract as a tube of varying cross-section excited by a series of pulse trains. The encoder tries to figure out the pulse information and from there derive the transfer function. For unvoiced signals such as fricatives it uses a simpler model excited by noise. The decoder then uses this information to regenerate the guessed-at signal. Lots of research has made to make these sound pretty good for reduced bit rates (typical bit rates 8-14 kbit/s). Most codecs can prioritize your bit allocations, so critical bits absolutely needed for intelligibility are encoded with robust error correction, the next most have CRC checksums and allowed to have errors (for example few lost or broken data packets does not make phone to crash or voice totally unuseable). In any case, voice codecs are not the best way of encoding a music signal. Feeding a music signal through for example GSM codes causes significant amounts of distortion. When thinking of how the codecs work and how much the data is compressed indeed it's quite surprising that music comes through as well as it does.

      Video communications

      The Holy Grail of wireless communications is ubiquitous wireless video. Hype has quickly been building around wireless video for the past few years. With 2.5G and 3G systems on the way, many have started to view the delivery of video content to mobile phones as one of the killer apps. The challenge, however, is making this work. Streaming video to a mobile phone places huge strains on the processing engine within these systems. The processing involved in streaming video applications can be divided into roughly two types of functions: control and transport (CT) and media decode (MD).The CT and MD functions have different processing requirements. CT is not computationally intense and mainly involves string parsing, data packet manipulation, and finite state machine implementation (suitable for normal microprocessors). The CTR functionality usually used protocols like real-time streaming protocol (RTSP) session control and real-time transport protocol (RTP) media transport. The MD functionality is much more computationally intense because of the sophisticated signal processing required by audio and video coding algorithms (suitable for DSPs or microprocessor with special multimedia instructions). In the next three years we will see wireless communication speeds go from the existing and rather pathetic 9600 bps to an impressive 384 kbps. This will come about with the implementation of Third Generation mobile networks or UMTS (Universal Mobile Telephony Services).

      • Gearing Up For Wireless Video with Compression - Sophisticated video compression standards, like MPEG-4 and H263, make realtime video streaming on wireless handsets a reality - but not without some complexity.    Rate this link
      • Wireless Video--Get The Picture? - Today, wireless video is in the transitional phase between the "advanced prototype" and "functional solution with practical application"--what Geoffrey Moore might call, "crossing the chasm." All of the enabling technologies currently exist and are either in the market, beginning to be deployed, or will become available over the next 18 months. There is little doubt that these technologies will make widespread, global wireless video a reality.    Rate this link
      • Wireless Videophones and Windows CE - The increase in wireless bandwidths over the next few years puts us on the verge of making wireless video as common as the cell phone in your pocket.    Rate this link

      Signal encryption

      • Secure Your Wireless Future - The recent trend toward Internet-enabled wireless devices has prompted rapid growth of the mobile-commerce (m-commerce) marketplace. For this market to really take off, users must feel comfortable transferring personal and financial information via their wireless Internet connection. As a result, the issue of security takes on renewed interest. Public-key-cryptography systems (PKCS), in particular, will play a central role in providing users with the required level of comfort they desire.    Rate this link

      Software in cellular phones

      • Software Bugs Mobile Phones - Until recently, software for cellular telephones has been developed entirely in-house, but the growing demand for more complex software is making the task more difficult. As a consequence, the industry is now frequently outsourcing software components, and introducing techniques to improve the development process.    Rate this link

      Electronics in cellular phones and portable communication devices

      Running a powerful, potentially power hungry, electronics device from small batteries for long time is a challenge. Paractically all cellular phone devices must incorporate sophisticated power management chips in order to maximize the time that batteries can operate between recharges, minimize charging times and improve the lifetime of the battery itself. Most cellular phones are built in such way that the battery and the charging electronics for battery charging is mostly built into the cellular phone. The cellular phone mains adapers are typically just simple mains adapters that give usually somewhat current limited unrgulated DC to the cellular phone. The votlage from mains adapter to cellular phone is typically in 5-10V range and the current rating us typically in 300-500 mA range. Using wrong type of adapter can damage some cellular phones.

      It is also a great EMC challenge to built a cellular phone, because this device includes a quite powerful ratio transmitter, radio receiver, digital electronics and senstive audio electronics all in the same tight package. Mobile-phone designers who build to the GSM standard must sufficiently reduce audio "buzz" so that it is inaudible to users. GSM cell phones use a TDMA (time-division multiple-access) time-slot sharing technique that results in high-power RF in the 800/900- or 1800/1900-MHz bands. The transmitter operating current when it operates is quite high (easily hundreds of milliamps to one amp) and it is taken in the pulses. Those pulses occur during a phone call at a repetition rate of 217 Hz and pulse width of about 0.5 msec. If current pulses couple to the audio circuitry, the harmonic-rich, 217-Hz signal results in an audible buzz. Users rarely encounter an audible buzz with most quality mobile phones on the market today. However, when a wired headset's signal lead gets too close to the phone's antenna element, the problem emerges even in quality phones. There can be a considerable amount of RF energu near a phone. At the highest power level setting (cell phone long distance away from base station), thre cen be up to 32 dBm (more than 1W) of RF power in a typical phone. And received signal levels as low as -40 dBm (less than 1 microwatt) impinging upon semiconductor junctions can create a strong buzz.

      Good layout must prevent RF energy from coupling into the audio and power traces. Prevention methods include shielding, ground design, and careful overall layout practice. Despite your best effort, some RF will couple onto audio traces. To prevent this energy from conducting into the audio amplifiers' semiconductor junctions many designs employ filtering methods, for example small bypass capacitors that bypass RF without affecting audio. Because cell-phone RF occupies bands in the vicinity of 900 and 1800 MHz, the best choices are those capacitors that are self-resonant at those frequencies. Typical values for this application?10 and 39 pF?have negligible effect on audio signals. Usually there are LC or RC filters at the headset, charger, and data ports to prevent connecting cables from acting as antennas and conducting coupled transmitted power into those points. It is common to use a single integrated passive component that includes an RF filter and often ESD protection.

      Personal Digital Assistants technologies

      In 1993, Apple Computers vowed to reinvent portable computing. The company promised an "all-being, all-knowing, all-doing" electronic device. It would serve as an address book, day planner, notepad, fax machine, pager. It was designed to be an easy to use electronic device in the palm of a human hand. Apple even devised a catchy, hi-tech name for this miracle machine- the Personal Digital Assistant, or PDA for short. After long waiting Apple released the world's first PDA, the Newton. The Apple Newton grabbed people's imaginations, but did not capture their wallets. Since then hordes of other companies attempted to take advantage of Apple's failure. Each one of them released their own version of what they think is the perfect PDA. Nowadays there are still many different PDA product from different companies available. Simplest are only like electroni calendars and notebooks, while most powerful ones have lots of processing power (like Compaq iPaq) and possibly communication functions in them (like Nokia Communicator).

      Mobile data

      Generally you can't use normal modem communicationsthrough celluar networks, but generally they havesome way to offer a similar service.Normal telephone line modems do not work in mostcellular teleohone systems in any acceptable way.Generally the radio noise in unaccpetable onanalogue cellular systems. And digital cellularphones use speech codecs which compress speech tosomewhat working soundgin speecs, but causequite weird thigns to some non-speech signals.For transferring data on digital cellular systems(like GSM) the designers of networks havedesigned special data service modes tocarry data on the cellular network.For example GSM network can carry data normallyup to 9600 bps (there are aalso higher speed high speedmodes available with some operators and equipments).The data interfaces on many cellular phones makethe phone appear to applications like it werea normal 9600 bps modem.

      Cellular phone safety

      Cellular phones are electronic devices that commununicate with the ceullar system base station usign radio communications. This means that they contain both radio receiver and transmitter. The transmitter cause RF field around the cellular phone. RF fields are non-ionizing radiations (NIR). ). Unlike X-rays and gamma rays, they are much too weak to break the bonds that hold molecules in cells together and, therefore, produce ionization. RF fields may, however, produce different effects on biological systems such as cells, plants, animals, or human beings. These effects depend on frequency and intensity of the RF field. By no means, will all of these effects result in adverse health effects. RF fields between 1 MHz and 10 GHz penetrate exposed tissues and produce heating due to energy absorption in these tissues. The depth of penetration of the RF field into the tissue depends on the frequency of the field and is greater for lower frequencies. Energy absorption from RF fields in tissues is measured as a specific absorption rate (SAR) within a given tissue mass. The unit of SAR is watts per kilogram (W/kg). An SAR of at least 4 W/kg is needed to produce adverse health effects in people exposed to RF fields in this frequency range. Most adverse health effects that could occur from exposure to RF fields between 1 MHz and 10 GHz are consistent with responses to induced heating, resulting in rises in tissue or body temperatures higher than 1C. Current mobile phone systems operate at frequencies between 800 and 1800 MHz. RF fields penetrate exposed tissues to depths that depend on the frequency - up to a centimetre at the frequencies used by mobile phones. RF energy is absorbed in the body and produces heat, but the body's normal thermoregulatory processes carry this heat away. All established health effects of RF exposure are clearly related to heating. While RF energy can interact with body tissues at levels too low to cause any significant heating, no study has shown adverse health effects at exposure levels below international guideline limitsCurrent scientific evidence indicates that exposure to RF fields is unlikely to induce or promote cancers. Exposure to low-levels of RF fields, too low to produce heating, has been reported to alter the electrical activity of the brain in cats and rabbits by changing calcium ion mobility. However, these effects are not well established, nor are their implications for human health sufficiently well understood to provide a basis for restricting human exposure. Scientists have reported other effects of using mobile phones including changes in brain activity, reaction times, and sleep patterns. These effects are small and have no apparent health significance. More studies are in progress to try to confirm these findings. The human exposure limits for mobile phones set by national organizations usually within international guidelines developed by the International Commission on Non-Ionizing Radiation Protection. These are based on a careful analysis of all scientific literature (both thermal and non-thermal effects) and offer protection against all identified hazards of radiofrequency energy with large safety margins.Rather than emission limits, the standard specifies exposure limits to radiofrequency EMR that regulate the rate at which the mobile phone user absorbs energy from the handset. This is known as the specific absorption rate (SAR). The SAR limit for all mobile, cordless and satellite phone handsets for sale in Australia is 1.6 watts per kilogram of tissue (averaged over 1 gram). There are differences in SAR levels between different mobile phone models. The SAR rating published by the manufacturer is the result of tests conducted at worst case scenario. The energy you absorb from your phone cannot exceed that level. In practice, the energy you absorb in daily use of your phone will vary and in many instances will be much less that the published SAR. This is because the phone only uses as much energy as is needed to communicate with a base station. If the base station is nearby, the phone will only use as much energy as is efficient to communicate with the base station. Mobile phone handsets and base stations present quite different exposure situations. RF exposure to a user of a mobile phone is far higher than to a person living near a cellular base station. However, apart from infrequent signals used to maintain links with nearby base stations, the handset transmits RF energy only while a call is being made, whereas base stations are continuously transmitting signals.Handsets: Mobile phone handsets are low-powered RF transmitters, emitting maximum powers in the range of 0.2 to 0.6 watts. The RF field strength (and hence RF exposure to a user) falls off rapidly with distance from the handset. Therefore, the RF exposure to a user of a mobile phone located 10s of centimetres from the head (using a "hands free" appliance) is far lower than to a user who places the headset against the head. RF exposures to nearby people are very low. RF exposure levels to a user from mobile handsets are below international guidelines. If you are concerned about radiofrequency electromagnetic radiadion (EMR) while using your mobile phone you may choose to use a portable hands-free device. These are sold as an accessory to your mobile phone.Base stations: Base stations transmit power levels from a few watts to 100 watts or more, depending on the size of the region or "cell" that they are designed to service. Base station antennae are typically about 20-30 cm in width and a metre in length, mounted on buildings or towers at a height of from 15 to 50 metres above ground. These antennae emit RF beams that are typically very narrow in the vertical direction but quite broad in the horizontal direction. Because of the narrow vertical spread of the beam, the RF field intensity at the ground directly below the antenna is low. The RF field intensity increases slightly as one moves away from the base station and then decreases at greater distances from the antenna.Both measurements and calculations show that RF signal levels in areas of public access from base stations are far below international guidelines, typically by a factor of 100 or more. Electromagnetic interference and other effects: Mobile telephones, as well as many other electronic devices in common use, can cause electromagnetic interference in other electrical equipment. Therefore, caution should be exercised when using mobile telephones around sensitive electromedical equipment used in hospital intensive care units. Mobile telephones can, in rare instances, also cause interference in certain other medical devices, such as cardiac pacemakers and hearing aids. Individuals using such devices should contact their doctor to determine the susceptibility of their products to these effects. Other risks of using cellular phone: Research has clearly shown an increased risk of traffic accidents when mobile phones (either handheld or with a "hands-free" kit) are used while driving. Technical electronics safety: Cellular phones operate at low voltage (typically at 3-6V voltage) so the voltages in them are not dangerous. Cellular phones contain rechargeable batteries, which include several potential electrical risks. The batteries in cellular phones are lov voltsge devices, but are capble of generating high current if short circuited. Such high currents can cause lots of heat to the batteyr set itself and to electronics device conneced to it if the short circuit happens there. The energy in cellular phone battery is enough to cause fire on severe short circuit situation. For this reason most barries include internal protection circuitry to avoid this. Nowadays Lithium Ion (Li-ion) is the fastest growing battery system, because it has high energy density and is lightweigh. Li-ion technology is fragile (the contents of battery is flammable) and a protection circuit is required to assure safety. There has been some reports that damaged Li-ion batteries have cought in some case fire and even cause small "explosions". The number of this kind of accidents has been very low compared to the number of batteries in use. So there is a risk, but is low. To be safe be careful when handling the battery pack and do not use damaged battery packs.

      Cellular phone jamming and detecting

      Movie theaters today just ask you to silence your cell phone. Cell phones are asked to be turned off in the aeroplanes and hospitals for safety reasons (they can interfere with plane or medical electronics).

      • Interception Technology May 'Capture' Your Cell Phone - The device works by duping a cell phone into thinking it's the "cell tower" of choice. Once the unit has "captured" the phone, the system instructs the phone to move to a channel that is not active in that cellular system, prohibiting the phone from receiving communication from its normal base station.    Rate this link

    1G Introduction

    First generation wide area wireless communication systems are characterized as analog radio systems and designed for voice transfer. 1G Techologies used frequency dividision multiple access (FDMA) to communicate, meaning simply that every call in one are uses their own channels for voice communication.This kind of systems were resiged and used in 1970s and 1980s. Examples of this kind of systems include AMPS, TACS, and NMT. Here is some more information on those systems.

    • AMPS stands for Advanced Mobile Phone Service. It is an analog cellular phone system used in North and South America. AMPS uses FDMA and operates at 800 MHz band. AMPS was introduced in USA at 1983.
    • NMT stands for Nordic Mobile Telephone. It is an analog cellular phone system deployed in more than 40 countries in Europe. NMT was the first analog cellular phone system (launched in the Scandinavian countries 1979). The system used originally 450 MHz band (NMT 450), but later when more capacity was needed, it was also adopted for 900 MHz band (NMT 900).
    • TACS stands for Total Access Communications System. It is a modified version of AMPS. TACS is used in UK, Japan and China.
    Analogue 1G systems use frequency modulation (FM) for speech transmission. The history of 1G systems is the following:
    • 1970?s Microprocessors were used in the implementation of cellular networks
    • 1971 The first public radio telephone network ARP in Finland was opened (no automatic switching)
    • 1981 NMT 450 (Nordic Mobile Telephone) network started operation in Scandinavia
    • 1983 AMPS (Advanced Mobile Phone Service) in the US
    • 1985 TACS network in the UK
    Analogue systems created the critical mass of mobile users. Analogue technology has small subscriber and traffic capacities, and the use of radio spectrum is profuse. The limitations of analogue radio network technology became, however, clear as the number of subscribers increased. The need for more advanced solutions was urgent especially in Europe, where numerous standards in a relatively small region caused cumulative problems due to increased mobility of radio telephone users.

    1G Introduction

    1G cellular systems refer to the early analogue cellular phone technologies. The early 1980.s marked the first use of wireless cellular systems. It was typical for this kind of systems that the systems were quite limited in performance, no fancy features and mostly country specific standards. 1G systems differed from the earlier radio networks in a couple of ways. The first generation (1G) cellular systems had increased capacity and greater mobility support than the early wireless radio networks. The 1G systems employed the concept of cellular coverage, where the coverage area is divided into small cells. This greatly increased the overall capacity of the entire network due to the ability to reuse frequencies.

    The first generation of wireless consisted mostly of voice traffic handled with analog techniques.For example NMT and AMPS cellular technologies belong to this category.

    NMT was the first widely used international cellular phone system. It was used widely in Northern Europe. The project started in late 1970's in a co-operation with Finland, Sweden and Norway. The first version of the network started at 1982. This operated at 450 Mhz frequency band and was named first NMT, later NMT-450. The use of this system has then speared to also other countries in Norhern Europe and some areas in Russia. There is also version NMT-900 that operated at 900 MHz frequency band. The use of NMT has pretty much stopped in the countries that started it originally (for example ended in Finland).

    The Bell Telephone company (US) introduced the first cellular public network AMPS (Advanced Mobile Phone Service) in 1978. It became a single standard for North America in 1982. Developed in the 1970s and deployed in the 1980s and still used today. These phones transmit voice as an analog signal without any encryption of scrambling. As a result, they can be eavesdropped upon using handheld scanners sold at places like Radio Shack. Analog systems are widely deployed throughout the US, especially in rural areas. Although analog cell phones are still sold but not a good deal, as analog providers generally charge a lot of money, the phones do not have good battery life, and the sound quality is generally poor. The big advantage of analog cell phones is that they have the best nation-wide coverage, but that?s changing fast. If you have an analog cell phone, you probably want to get a new one. Nowadays there are ?dual-mode? digital phones that also support analog AMPS system for roaming in remote areas.

    2G Introduction

    Second generation (2G) cellular phone system use digital communication methods. They are capable of providing voice, data and other services. Digital technology combined with harmonized standardization has made it possible to make calls at any time, anywhere, and both speech and data can be transmitted and received.The second generation (2G) wireless systems are characterized by the use of digital radio transmission. The increase in system capacity was due to the use of hierarchical cell structures and the ability to use a single frequency channel for multiple users (code and/or time division).Examples of this series of systems include GSM, D-AMPS (TDMA/IS-136) and CDMA IS-95-A. Here is some more informatiom on those system.

    • GSM stands for Global System for Mobile Communication. It was originally designed for operation at 900 Mhz band, bu has been later adopted for other frequency bands also. GSM variations are used in Europe, Asia and North America. Nowadays GSM products are operating at 900, 1800 and 1900 MHz (some people have also though of 800 and 450 MHz versions sometimes). GSM supports voice and data communications. Typical maximum data rate is 14.4 kbps. GSM system uses TDMA access with 200 kHz channels divided into eight time slots, with two slots (in different channels) used to send and receive signals.
    • D-AMPS stands for Digital-Advanced Mobile Phone Service. It is a digital version of AMPS. D-AMPS is also known as TDMA/IS-136. D-AMPS is mostly used in USA. D-AMPS cellular phones transmit in the 824-849 MHz range and receive in the 869-894 MHz range using 30 kHz channels (FDMA). In addition to this TDMA is used to create time slots within each channel.
    • TDMA (Time Division Multiple Access) is the digital telephone standard that was deployed by AT&T in the 1990s. AT&T?s telephones have a ?voice privacy? or ?voice security? setting which enables encryption, but the network did not seem to support this.
    • CDMA-95-A is a cellular phone system that uses CDMA radio communication to be able to dend multiple signals in the same channel (a form of multiplexing). This system used spead spectrum (DS/SS) tecnology to vaty the transmit frequency according the code pattern. CDMA-95-A supports data speeds up to 14.4 kbps. An updated version of it, know as CDMA-95-B supports speed up to 64 kbps.
    The 2G systems has been increased in the features over years. Enhancements upon this second generation of wireless systems (termed .2.5G.) has increased system capacities even further. These enhancements give for example better voice quality, faster data transfer and packet mode data communications.Present 2.5G systems satisfy our current needs at year 2003.

    GSM

    The Europeans realized rapid growth of cellular communications early on, and in 1982 the Conference of European Posts and Telegraphs (CEPT) formed a study group called the Groupe Sp?cial Mobile (GSM) to study and develop a pan?European public land mobile system. In 1989, GSM responsibility was transferred to the European Telecommunication Standards Institute (ETSI), and phase I of the GSM specifications were published in 1990. Commercial service was started in mid?1991, and by 1993 there were 36 GSM networks in 22 countries.The most basic teleservice supported by GSM is telephony. From the beginning, the planners of GSM wanted ISDN compatibility in services offered and control signalling used. The digital nature of GSM allows data, both synchronous and asynchronous, to be transported as a bearer service to or from an ISDN terminal. The data rates supported by GSM are 300 bps, 600 bps, 1200 bps, 2400 bps, and 9600 bps (14400 bps was added later). Group 3 fax, an analog method described in ITU?T recommendation T.30 is also supported by use of an appropriate fax adaptor.GSM features:

    • Maximum data rate: 9600 bit/s (there are some extension that allow now faster speeds)
    • Maximum mobile terminal output power: 8 W
    • Maximum hand-held mobile terminal output power: 2W
    • Maximum cell radius: 30 km
    • Minimum cell radius: 350 m
    • Access method: TDMA/FDMA
    • Number of radio channels in each direction: 124
    • Number of speech channels per radio channel: 8
    • Modulation: Minimum Shift Keying (GSMK)
    GSM system uses a combination of time division multiple access and frequency division multiple access to use the radio spectrum. TDMA is used to divide one carrier frequency to up to 8 users. Different frequencies are used ot be able to have many different frequency carriers on the same location to get more capacity than 8 users. Transmitting and receiving uses different frequencies. The common channel structure is a total of 156.25 bits, transmitted every 0.577 milliseconds, giving a gross bit rate of 270.833 kbps. This bit rate is then divided with the data from 8 users, control data, time delay control spare bits and bits used for equalization. A unique feature of GSM compared to older analog systems is the Short Message Service (SMS). SMS is a bidirectional service for sending short alphanumeric (up to 160 bytes) messages in a store?and?forward fashion. For point?to?point SMS, a message can be sent to another subscriber to the service, and an acknowledgement of receipt is provided to the sender. SMS can also be used in a cell?broadcast mode, for sending messages such as traffic updates or news updates. GSM History:
    • 1978 Frequency allocation by CEPT
    • 1982 Group Special Mobile within CEPT
    • 1987 GSM group described the main technical options for the mobile radio telephony standards
    • 1987 GSM MoU (Memorandum of Understanding)
    • 1990 Phase 1 specifications were frozen
    • 1992 First GSM networks in commercial use
    • 1992 Phase 2 specifications
    • The first public GSM call in the world took place on the 1st of July, 1991 (Finland)

    Network operators in most of the world use the original GSM spectrum allocation at 900 MHz. The frequency range allocated for ceullar telephy purposes (used now by GSM) in the 1978 World Administrative Radio Conference (WARC) was 890-915 MHz for transmissions from mobile stations and 935-960 MHz for transmissions from fixed stations. Additional spectrum at 1,800 MHz is used for the GSM derivative called DCS-1800, and this band is used in many countries. Some countries with cellular allocations at 450 MHz may begin deploying GSM in that band as well to replace old analog networks. In many areas of the United States, there are GSM systems operating in the 1,900- MHz PCS frequency band. There are also plans to make GSM standards for operation at 400 MHz and 800 MHz bands. The practical use of different frequencies is nowadays the following: In Europe the GSM networks generally use 900 MHz frequency band throughout Europe. Quite many countries also use 1800 MHz frequency on places like large cities where the capacity available at 900 Mhz frequency band is not enough to cover the needs of the users. Many modern European GSM phones are built as "dual-band" phones, that can use both of those frequency bands, and automatically transparently to the user switch between those frequency bands as needed (controlled by the operator).In USA GSM networks use 1900 MHz frequency band. This frequency band was selected to be used there, because the 900 MHz and 1800 MHz frequency bands were already used for other purposes. Considering the many options available, dual-band GSM phones are quite commonplace now. A few tri-band (900/1800/1900 MHz) phones are also available, allowing a GSM subscriber to use the same phone almost anywhere in the world.

    Circuit-switched voice calls are still the most commonly used services in GSM networks. Users use also data services. Current datacom services over GSM generally allows transferring files or data and sending faxes at 9.6 kbps. This current data communication in GSM network is circuit switched.

    GSM phones are designed to work at ground level or quite near to earth with users moving at reasonable speed (maximum speed 500 km/h or so). The GSM system is not designed to work in aeroplanes and trying to use cellular phone in aeroplane is not a good idea (it is generally not allowed). The problem is that at very high altitudes, the phone "sees" tens or hundreds of cell base stations at once, and the system isn't really designed to deal with this. Even if one cell can decide it will take the initial call, cell switching will be occurring every few seconds as the signal strength fluctuates. The problem multiplies if you are crossing those cells at 500mph. Trying to in-flight GSM phone calls is a bad idea. The system is designed on the assumption that calls will be made on the ground, therefore range-limited, and thus can only possibly be routed by one or two base stations, not hundreds. Other peoblem for in flight calls is that the GSM phone can potentially interfere with the electronics on board in the plane, which is not a good idea.

    There are many GSM operators operating at different countries, and even in many locations there are several different operators that compete against each other on the same are. In GSM system there is a feature called "roaming" available. It allows you to use the network of some other operator to make calls instead of your own operator that muight not be reacable (for example when youre abroad). If you roam into an area not covered by your home network your handset looks for networks that your network operator has made a "roaming agreement." If the network(s) that are found allow you to register you can use them (because your home carrier has made a roaming agreement with the carrier that you are visiting.) If no roaming agreement is present you cannot use that network and only can make emergency (911/112) calls.

      Enhanced GSM data

      There are two basic modes of data access over a wireless network: circuit switched and packet switched. In circuit switched system connection is a dedicated connection, and the user is billed, using the same method as that used for a voice call, by the minutes of usage. Current datacom services over GSM generally allows transferring files or data and sending faxes at 9.6 kbps. This current data communication in GSM network is circuit switched. The existing GSM network provides data access at speeds up to 14.4 kbps. This was considered a reasonable speed when the system was developed. In packet switching data streams are broken up into packets, each packet is then quickly routed to its destination over a shared medium. Billing is done on a cents-per-packet basis, independent of the time spent online. Enhanced GSM data technologies promise more transfer speed and also packet mode transmission.

        GPRS

        GPRS is an extension of the GSM system, and uses the same channels, the same modulation, and the same network backbone as the existing GSM network.

        High Speed Circuit Switched Data (HSCSD)

        High Speed Circuit Switched Data (HSCSD) is a new high speed implementation of GSM data techniques. HSCSD allows wireless data to be transmitted at 38.4 kilobits per second or even faster over GSM networks by allocating up to eight time slots to a single user.

        • High Speed Circuit Switched Data (HSCSD) - High Speed Circuit Switched Data (HSCSD) is a new high speed implementation of GSM data techniques. HSCSD allows wireless data to be transmitted at 38.4 kilobits per second or even faster over GSM networks by allocating up to eight time slots to a single user.    Rate this link

      Short messsage service (SMS)

      SMS is a bidirectional service for sending short alphanumeric (up to 160 bytes) messages in a store?and?forward fashion. For point?to?point SMS, a message can be sent to another subscriber to the service, and an acknowledgement of receipt is provided to the sender. SMS can also be used in a cell?broadcast mode, for sending messages such as traffic updates or news updates. Short messsage service (SMS) is a messaging method included in GSM system which allows sensing short messages from one cellular phone to another. GSM Short Messages have a maximum length of 160 characters (from the SMS character set), or 140 octets. However, Short Messages can be concatenated to form longer messages. Besides normal text based user to user messaging SMS system has been used to impement interfaces to on-line services and for carrying other kind of data (like alarm tones and logos to certain GSM phones). Short message service (SMS) is a globally accepted wireless service that enables the transmission of alphanumeric messages between mobile subscribers and external systems such as electronic mail, paging, and voice mail systems. SMS has also been used for tranporting data like cellular phone ring tones and screen logos (for example in Nokia Smart Messaging system). SMS messages can be sent in several ways. The most typical way the users send them is that they type those messages with their cellular phones and then send them from it. There are also other ways to do this. The automated SMS based services need a computerized way to do the same thing. There are several ways how a SMS can be sent from a computer. One of the simplest method for small volume SMS traffic sending is to use a GSM modem or GSM phone connected to a PC serial port. With a suitable software you can send SMS through them from computer. For higher volume SMS sending quite many operators also provide a computer interface that allows sending messages directly from computer to SMSC (Short Message Service Center). There are several protocols that are designed for this. Examples of such protocols that can be used are SMPP (Short Message Peer to Peer), CIMD, UCP/EMI (Universal Computer Protocol / External Machine Interface) and HTTP (Hyper Text Transport Protocol).

      Building systems for hadling SMS messages

      • Mobile Network Services with Linux - The skinny on building your own SMS gateway    Rate this link
      • Remote Control Module BieneRemote01 (OEM) - Home Automation control via SMS message. You can receive text messages with the occurrence of an event automatically to GSM mobile (cell) phones. You can transmit command messages and switches the output - switch on/off remote equipment. This is introduction to one product for this and reading this article is also a good introduction what can be done in this